Conversion of human waste into biochar using pyrolysis at a community-scale facility in Kenya (Stanford University and Climate Foundation, USA and Kenya)
26 Aug 2013 13:43 #5430

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Dear all,
I'm Laura Talsma, working for the Climate Foundation on bridging the technology development in the US with its end users and biochar markets in East Africa. I've started working for this team in the phase 2 of the Reinvent the Toilet Challenge, which I'll tell you more about soon, but for now some of the results of the completed Phase 1.

Let me start with a photo of the project team for Phase 1 (I'm not on the photo because I joined for Phase 2):

We’d like to introduce this project, related to the conversion of human solid waste to biochar, in the first phase of the Reinvent the Toilet Challenge funded by the Bill & Melinda Gates Foundation. The project is aimed at eliminating the risk of human waste, and creating a resource from it at the same time - biochar as a soil amendment in agriculture is a very valuable substrate for nutrients, and can retain water in the soils.

The Human Solid Waste (HSW) Biochar Reactor Project will demonstrate an economic value chain that converts human solid waste from thousands of people into agricultural fertilizer substrate in a single day.

Figure below: Overview of the biochar reactor for treating human solid waste (HSW); the HSW is gasified, thus producing syngas. The syngas is burnt to pyrolyse the HSW on a rotating plate, and thereby sanitize it. The biochar produced is completely pathogen-free.

Name of lead organization: Stanford University & The Climate Foundation (www.climatefoundation.org/)Primary contact at lead organization: Brian Von HerzenGrantee location: Stanford, California, USADeveloping country where the research is being or will be tested: Kenya

Goals:
The goal of this project is to design, build, and test a self-contained system that can pyrolyze (decompose organic material at high temperatures without oxygen) human solid waste into a type of biological charcoal (biochar) that captures and stores carbon. The design target of phase 1 was to deliver a proof of concept of the technology, towards the ultimate goal of processing two tons of human waste daily at a facility located in the slums of Nairobi.

Short description of the project:
In the Reinvent the Toilet Challenge (RTTC), researchers from all over the world are challenged to come up with a radical new technology for treating human waste, and eventually making it accessible for the whole world. Just treatment is not enough though; the solution has to be affordable, and has to produce valuable elements from the waste - either energy, clean water, nutrients, or all. Phase 1 of the RTTC was aimed at proving the feasibility of the technology; in August 2012, a working prototype of the biochar reactor was demonstrated at the Reinvent the Toilet Fair at the headquarters of the Bill & Melinda Gates Foundation. Together with Sanergy in Nairobi, the technology will be developed further to make it ready to process human waste on a large scale in Kenya.

Funding for this research currently ongoing (yes/no): yes (Phase 2)Research or implementation partners: Stanford University

Figure below: The syngas burning, causing the pyrolysis of the HSW.

Figure below: the biochar produced by HSW; sanitized, and ready to use as a soil amendment.

Current state of affairs: The first phase of the biochar reactor development has been completed, showing the feasibility of using a biochar reactor for processing human waste. At the moment, a second phase of the project has been granted and started.

Biggest successes so far: The demonstration of a functional prototype human solid waste biochar reactor at the Reinvent the Toilet Fair in Seattle, August 2012.
The Phase I design has only one primary moving component, reducing complexity and possible failure modes. The reactor is relatively simple to operate, maintain and repair. The semi-continuous combustion of syngas from a HSW simulant input material stream, allowing for self-sustained, net-energy-positive operation.

Main challenges and opportunities:
Agile prototyping relies upon accessible modification of reactor designs and implementations. The biochar reactor can be built with more elegant resealable sealing. We are further investigating alternatives to our current gas-tight high-temperature sealing strategy.

There was syngas flammability variability across the fully anticipated range of operation of the reactor, due to incomplete mixing while using high moisture content HSW simulant. There will be a strong focus on pre-drying the material in the Phase II system.

I was just wondering if or when you plan to start testing this technology in Kenya? I'm working with Water For People on bringing new sanitation technologies to the market in Uganda and pyrolysis is something I'm quite interested in as a concept.

What are you planning to use as your feedstock? Will you use pit sludge or solids from a low-volume collection system a-la Sanergy or Ghanasan/Cleanteam? What's the moisture content you need for this to be viable and what's the target cost for your technology?

Re: Conversion of human waste into biochar using pyrolysis at a community-scale facility in Kenya (Stanford University and Climate Foundation, USA and Kenya)
26 Aug 2013 14:40 #5434

Bridging the gap between technology development in US and deployment in East Africa, for a waste to energy solution by the Climate Foundation

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Hi Dan!

Thanks for your reply. We're at the moment in phase two of this project - scaling up the proof of concept of the first phase into an operational prototype. The technology is still under development, but we're aiming to test the prototype at Sanergy in the second quarter of 2014.
The feedstock used is the solid waste picked up by Sanergy. We're determining the moisture levels and variation in it at Sanergy, so the biochar reactor can be adapted to it. As for the equipment target cost, I'll have to get back to you - we will know more in a couple of months.

I read your grant description with interest; what I found most interesting was the usage of biochar as a soil amendment but not as an energy source. I would like to ask couple of questions regarding to your interesting project.

1 - How did you choose ultimate processing capacity of 2 tons per day? Did you plan to serve for a specific slum area or it was just a general capacity of your system? If you targeted a specific slum area, what is the population of this slum area? What is the maximum waste amount that you have processed until now?

2 - What is the ratio of biochar production to inlet fecal matter?

3 - Also, have you done any analysis on application ratio of biochar per soil mass (how much biochar should be applied to the soil for achieving optimum agricultural yield)?

Thanks in advance,

Gökce

M.Sc. Gökce Iyicil
Research Assistant
Technical University of Munich
e-mail:
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www.tum-ias.dewww.sww.bv.tum.de

Thanks a lot for supplying us with so much Information. It is indeed very interesting work.

In contrast to Gökce, I was not surprised that your also looking into using the charred faeces as a soil conditioner (e.g. University of Colorado funded by BMGF). I was wondering about the marked demand. I assume you target urban slums, where, the demand for soil conditioner is rather low compared to energy. I feel in the urban context, large-scale pyrolysis factories processing urban organic solid waste (excreta, faecal sludge, sewage sludge, organic municipal solid waste, waste from urban agriculture) to produce bio-coal briquettes might be a more viable market segment. What do you think?

Re: Conversion of human waste into biochar using pyrolysis at a community-scale facility in Kenya (Stanford University and Climate Foundation, USA and Kenya)
02 Dec 2013 17:57 #6603

Bridging the gap between technology development in US and deployment in East Africa, for a waste to energy solution by the Climate Foundation

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Dear Moritz and Gökce!

I'll try to reply to your messages both at once - since they're quite related.

Actually I've recently returned from Kenya to do the first market demand research on the different products we could make with biochar. I was surprised to find an existing market for both biochar briquettes and biochar as a soil conditioner. In our lab at Sanergy in Nairobi together with Cornell in the US we're researching the properties of the biochar we're making from human waste - those properties will also determine which market segment we'll target. There's a big market for fuel briquettes in the urban areas, close to where a lot of the waste is, which reduces transport costs. At the moment we're still considering both options - the margins for soil conditioner are much higher, but have additional transport costs. Briquettes tend to sell for less, but markets are close.

For some of the quantitative questions of Gökce:
- the 2 tonnes are derived from Sanergy's waste infrastructure at the moment, as we're piloting with them. It's always a balance between the benefits of a larger scale and the feasibility and costs of collecting and processing locally..
- The conversion of human waste into biochar: the feed is around 70% wet, part of the biochar reactor is an energy efficient drying bed to dewater the waste. Biochar reactors on other feedstocks produce 25% of biochar from the dry waste mass - as we're producing an energy neutral system, we'll have to use part of that biochar to run the machine, so we'll have a lower efficiency.
- The biochar needed for optimal agricultural yield is another big question - we've visited several biochar research sites in Kenya, and talked to the main professors working on biochar - but the optimal application rates are not set in stone (yet). Dependencies are on soil conditions and location - and carbon content can be built up over time. The research sites used between 1-4 tonnes of biochar per acre, and some new mixes are being developed with biochar and compost, or other nutients added.

Bridging the gap between technology development in US and deployment in East Africa, for a waste to energy solution by the Climate Foundation

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After months of hard work to get everything ready in time, Climate Foundation and partners were proud to show a working biochar reactor prototype at the fair in Delhi, in March.

During the fair, many interested visitors could take a look at the processing technology from close by. Human waste simulant provided by the Gates Foundation was dried at the belt drying system, and charred in the biochar reactor.

Currently, the reactor is further integrated, tested and improved in our workshop in Bangalore, before being shipped off to Nairobi for trials later in the year.

Take a look at our videos from the fair and technology introduction!

Complete system overview, R&D activities, lab research at Sanergy/Cornell and market research in Kenya:

Bridging the gap between technology development in US and deployment in East Africa, for a waste to energy solution by the Climate Foundation

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Dear all,

In case you have been following this thread and are interested in the progress of our research project, then the upcoming webinar number 7 on “Adding missing links in sanitation value chains” could be interesting for you:

Our presentation is entitled:

Community-scale facility to process faeces and faecal sludge into safe biochar by pyrolysis – preparing for field testing with Sanergy in Nairobi

There is no need to download any software to attend (simply go to this website: seint.adobeconnect.com/seiwebinar/). However, you must obtain the password to enter the room. To obtain the password, please e-mail Elisabeth von Muench:
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.

We look forward to meeting you at the webinar and answering any questions you may have. If you have questions about the content of the research before the webinar, please put them here on the forum.

We had a great webinar yesterday with 50 participants (new record) and 3 excellent teams giving presentations about their research! Over the course of the next few days, I will share information from the webinar with you. I will start here with some information about the project by the team of Climate Foundation. The recorded videos will also be available soon.

This is the presentation that Laura and Brian used, with the title"Community-scale facility to process faeces and faecal sludge into safe biochar by pyrolysis – preparing for field testing with Sanergy in Nairobi":

This attachment is hidden for guests. Please log in or register to see it.

And here is the log from the chat:

Edit on 16 May: I have removed the chat log here, find instead a better structured summary of the chat below in Laura's post from 15 May 2014.

++++++++++

Thanks again to all presenters and participants! Further questions or comments by anyone, please do put them here, thanks.

(note: there is no sound for 17 seconds starting at 2:59 - our apologies)

The video includes the presentation as well as a question and answer session, which I briefly summarise below:

(1)
A question was asked by Mutala about social acceptance of the biochar product (given that it was made from human excreta).

Brian explained that they are thinking of going for crops like cotton, flowers, fruit trees, as reuse might be easier to accept there (risk even reduced further, even though pathogen inactivation will be complete at those temperatures in the biochar reactor).

(2)
Question by Marc Dehusses: what's the power of the Stirling engine?

Answer: Stirling engine on average 18-20% efficiency. 45 kW of thermal energy will go into the Stirling engine. There is 10 kW of electrical energy available to run the system. As less than 10 kW electrical energy will be required to run it, there will be a surplus of both electrical and thermal energy. - Start-up would be with conventional charcoal.

(3)
Question by myself: why the connection with Sanergy, did you build this process around the Sanergy setup?

Answer by Brian: Yes, the decision to work with Sanergy was made right at the start (Sanergy was inspiration to their model). From a pyrolysis perspective, this is fundamentally a moisture problem. Hence UDDTs make a lot of sense (why add moisture to the excreta if you don't have to). Also it's a nutrient conservation issue (nitrogen capture in the UDDT via the urine and faeces). UDDTs have strong benefits amd make a lot of sense at least from a thermodynamic standpoint.

In the general discussion video, Brian was asked a question about the smallest possible size for this system.

Brian explained that their first version was for 100 users but the smaller systems have more thermal losses (greater surface area to volume ratio). Their current system is designed for daily excreta from 2000 people.

Brian also explained that in the villages, perhaps municipal solid waste, green waste could be taken as additional inputs (moisture level is lower than for faeces - net moisture level at 60%).
Laura pointed out that it needs a certain scale to make it interesting for the entrepreneurs. Sanergy is their first client.

I hope you found this summary of the discussion from the Youtube videos useful.

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Thanks again, everyone for attending the susana webinar and posing good questions. We organized the questions per topic and added some more info. Let me know if you have any follow-up questions!

Biochar Q & A from SuSaNa Webinar - April 29th 2014

Scale of Population Served

What population is served with this processing technology? (what is the scale of the system) Arno Rosemarin: What is the optimal population/user number size for this system? Elisabeth von Muench: What does 100 kg of human excreta per hour translate to in terms of number of people served?Laura Talsma: The system is designed to process up to 100 kg of feces per hour, which serves approximately 250-1000 people each hour (assuming 100g-400g per person/per day of solids).

Energetics

Marc Deshusses: What's the power of the Stirling engine?Brian von Herzen: Marc: the Stirling can generate at least several kW under typical conditions.

ARNO ROSEMARIN: Will we be able to heat cities with this type of reactor also burning solid waste organics?Brian von Herzen: Arno: cogeneration is certainly possible, yes.

How does the energetic conversion of the pyrolysis look like? Can it work off the grid?Elisabeth von Muench:[/b] I am still really puzzled that you can do this without external power input. Is it because you take an input that is already relatively dry? I.e. only up to 70% moisture content?Gerhard Muggen: it would be estimation that there is too much moisture to get an energy positive output.Laura Talsma: Gerhard - good question - we are using the moisture level found in human feces, validated by sanergy, which is in the 70%-75% range.Laura Talsma: We'll test in bangalore as well with higher moisture levelsGerhard Muggen: I would estimate that you could only have a positive energy output if you have max 60 % waterLaura Talsma: Gerhard - we're recapturing also the heat of condensation from the carbonizer, that combined with an energy-efficient biomass dryer helps with thermal energy balanceBrian von Herzen: Gerhard, we would be happy to share the energetics with you, at 20 MJ/kg there is energy available to dry the feces. <Brian sent energetics info to Gerhard - details are available on request at
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>Brian von Herzen: I can assure you the energy balance is significantly above 60% moisture level.

Biomass Input and Biochar Output

Mutala Mohammed: What is the ratio of the quantity of human excreta to biochar production?Laura Talsma: Mutala - at most 25% of the dry mass going in comes out as biochar.

Elisabeth von Muench: The sawdust used by Sanergy to mix with human waste also helps in getting sufficient energy into the reactor - have you ever calculated what would happen if – for whatever reason – Sanergy stopped adding the saw dust at their end? Would you then need external charcoal to power your process?Brian von Herzen: No, toilet paper contributes in the same manner as sawdust. And there are a number of biomass inputs that can replace the sawdust cover material as needed. We can use the internal biochar created by the reactor and do not require external charcoal.

Mutala Mohammed: Are all the pathogens removed in the process?Laura Talsma: Mutala - the feces are heated to 300-700 degrees C, enough to kill all pathogensBrian von Herzen: Mutala, since the process ensures that all material exceeds 300C, all pathogens are removed.

Economics

Elisabeth von Muench: Would Sanergy add the costs for this biochar reactor somehow onto their operational costs, or I guess the hope would be to recover the costs via selling of the biochar?Laura Talsma: our current business model includes the sales of the biochar, with an addition of a sanitation contribution of some cents per person. The business case depends on the value of the biochar in the country you’re working in.

Elisabeth von Muench: How much biochar would there be for sale compared to the biochar you would need to energise your process? Can it be expressed as a ratio or percent?Brian von Herzen: 25 Kg dry feces is about half carbon. Of the 12.5 Kg of carbon, less than half can provide biochar, so a maximum of 6-7 Kg.Brian von Herzen: Elisabeth: the energy surplus is a strong function of the moisture level. Below 70% there should be a strong excess energy as the moisture level approaches 80%, the energetic surplus shrinks.

Community Impact and Acceptance

Jeremy Kohlitz: How much noise does it make?Laura Talsma: Jeremy - we have blowers transferring air through the human waste, and after that through the biochar filters, which act as mufflers - there is a sound, but it's not too loud, can be used in middle of slum. The noise is determined mostly by the drying air, and thus would be comparable to a ventilation system for a building.

Mutala Mohammed: But I think the social behaviour of people in Africa is key in the success of this project.Mutala Mohammed: People’s perception of the use of faecal sludge products is a major challenge in the promotion of such technologies in AfricaLaura Talsma: Yes, Mutala, definitely, it will depend on the acceptance of the end products. The benefit is that the biochar end product is odorless and similar to wood charcoal in appearanceLaura Talsma: we're testing these kind of acceptance challenges now with farmers in Kenya, together with SanergyElisabeth von Muench: Mutula: the biochar looks so similar to "normal" char, do you really think people would have a problem with burning it?Mutala Mohammed: We did a similar field trials and our major obstacle was the acceptance of the product by the local people.Laura Talsma: that's very interesting - Mutala, where did you do the trials?Mutala Mohammed: We did the trials in University of science and technology (KNUST) in GhanaBrian von Herzen: one key that i have learned is that we have to validate the sanitation level and prove how sterile the biochar is and, for example, demonstrate to people that biochar from solids is safeBrian von Herzen: We can start with non-food crops and trees, and once demonstrated it can expand to other food crops once confidence is built.